A fire retardant door--often referred to as a fire door--is installed in a building for preventing the spread of fire from one part of the building to another. To fulfill that purpose a fire door must be made substantially entirely of incombustible material. But a fire door must also be regarded as part of the interior of a living space, and as such it must be aesthetically satisfactory. Usually, therefore, the core of incombustible material that comprises the main structure of a fire door is overlain with a thin wood veneer facing that provides it with a desirably attractive appearance.
For safety reasons as well as for admission of light, a fire door is often provided with a window, usually having a glass pane in which a wire mesh is embedded. This pane should be sealed around its edge to the incombustible core of the fire door, and for aesthetic reasons as well as to ensure the necessary seal, should be surrounded by a suitable frame or bead. Various types of metal frames have been devised for fire door windows, some of which provide for securement of the pane to the fire door core as well as for trimming the margin of the pane and the edges of the hole in the door in which the pane is installed. Such metal frames must be painted to match or simulate the wood of the door facing, requiring a special finish different from that applied to the wood. A metal frame is seldom as attractive as a wood frame would be. Furthermore, any slight chipping or abrasion of the painted surface of a metal frame exposes the metal and tends to make the whole door unattractive.
U.S. Pat. No. 2,927,353, to Snitker, discloses a windowed fire retarding door wherein the window pane is secured and sealed to the door structure by means of a body of incombustible material which is initially in slurry form and in which the marginal portions of the pane are embedded all around the pane. The arrangement as disclosed is not objectionable in appearance, but it is not particularly attractive. More important, embedding the pane in the incombustible material requires that the pane be supported in some manner, to be held in the proper position and attitude relative to the door frame until the slurry has set up or hardened to a substantial extent, and this requirement greatly complicates manufacture of the door because the pane must be supported at portions of it that are not embedded in the slurry.
As is suggested by the deficiencies in Snitker's teachings, the provision of satisfactory means for supporting, sealing and trimming the pane in a windowed fire door requires an arrangement that is not only aesthetically attractive and structurally sound but is also capable of fast and easy installation, preferably by one person and with the use of simple conventional tools. Heretofore there has been no expedient for the purpose which has fully satisfied all of thse requirements.